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INTRODUCTION
In a mild winter climate like that of the Mediterranean region, flowering and cropping of fruit trees depended highly on winter chill (Campoy et al., 2011; Viti et al., 2010). Fruit tree cultivars have specific genetic chilling requirements to break dormancy (Alonso et al., 2005; Egea et al., 2003; Ruiz et al., 2007). Lack of chilling in warm winter regions results in abnormal patterns of bud break and development in fruit trees (Ben Mimoun, 2008; Campoy et al., 2012; Crossa-Raynaud, 1955; Erez, 1987, 1999; Erez and Couvillon, 1987; Legave et al., 1982; Viti et al., 2010). Several dormancy-breaking agents were used to stimulate bud break of deciduous fruit trees in warm areas lacking sufficient chilling accumulation (Campoy et al., 2010; Jackson and Bepete, 1995; Mohamed, 2008; Seif El-Yazal and Rady, 2012; Theron et al., 2011). The agents included growth regulators, gibberellins, cytokinins mineral oils and potassium nitrate. However, hydrogen cyanamide (Dormex®) is considered as an efficient solution for breaking dormancy and having synergistic effect on bud break, flowering, yield and fruit quality (Bartolini et al., 1997; Erez, 1987; Jackson and Bepete, 1995; Seif El-Yazal and Rady, 2012).
The rest-breaking effect is both dosage- and time-dependant, with stronger effects at higher concentrations and later applications (Erez and Lavee, 1974). Timing of application of cyanamide cannot be safely done as in the case of oil-dinitro-o-cresol (DNOC), but should be allowed 30 days before bud swell (Erez, 1995). George et al. (1992) found that early applications of cyanamide on peach are usually more effective in advancing floral and vegetative bud break than applications closer to normal blooming. High concentrations of cyanamide on stone fruit species lead to a marked advancement of leafing over bloom, which may have negative effects on fruit set due to sink competition (Erez, 1995). Erez (1987) discourages applications of cyanamide within less than four weeks of bud swell, especially where maximal level of bloom is desired as in the case of small fruits and nuts. The range of 2-4% Dormex® was successfully applied on many fruit trees (Bartolini et al., 1997; Erez, 1995; Shulman et al., 1986).
Pistachio (Pistacia vera L.) is...